Method for reforming hydrocarbons

ABSTRACT

Alumina particles derived from hydrous alumina predominating in α-alumina monohydrate having a crystallite size of less than 100A and having increased porosity can be prepared by a process which comprises forming a mixture of an aqueous slurry of the hydrous alumina and at least one surface active agent, drying this mixture, forming macrosize particles from the dried mixture and calcining the macrosized particles.

This is a division, of application Ser. No. 205,355, filed Dec. 6, 1971,now U.S. Pat. No. 4,066,740.

This invention relates to improved alumina and alumina-based particles.More particularly, the invention relates to the manufacture of aluminaand alumina-based particles having improved physical properties andbeing useful, for example, as catalysts and catalyst supports.

Alumina-based catalysts are useful in many industrial applications,e.g., petroleum reforming and desulfurization, aromatization, paraffinand aromatic hydrocarbon isomerization and the like. In many of theseapplications the activity of the alumina-based catalyst is directlyrelated to the porosity, i.e., pore volume per unit weight, of thealumina support. Therefore, it would be advantageous to provide aluminaand alumina based particles having increased porosity.

Therefore, it is an object of the present invention to produce aluminahaving increased porosity. Another object of the present invention is toprovide means by which the porosity of alumina can be altered andcontrolled. Additional objects and advantages of the present inventionwill become apparent hereinafter.

It has now been found that alumina and alumina-based particles derivedfrom hydrous alumina predominating in α-alumina monohydrate having acrystallite size of less than 100A units having increased porosity canbe prepared by a process which comprises:

(1) forming a mixture of an aqueous slurry of the hydrous alumina and atleast one surface active agent, the surface active agent being presentin the mixture in an amount sufficient to increase the porosity of thecalcined alumina hereinafter described;

(2) drying said mixture to obtain a solid product which can be formedinto macrosize particles;

(3) forming said solid product into macrosize particles; and

(4) calcining said macrosize particles to form calcined aluminaparticles having increased porosity.

The mixture formed in step (1) normally contains from about 1% to about50%, preferably from about 1% to about 16% and more preferably fromabout 8% to about 14%, by weight of alumina (calculated as Al₂ O₃). Theaqueous slurry of hydrous alumina may be prepared by various methodswell known to the art. Thus, for instance, hydrated alumina can beprecipitated from an aqueous solution of a soluble aluminum salt, suchas aluminum chloride. Ammonium hydroxide is a useful agent for effectingthe precipitation. Control of the pH to maintain it within the valuesfrom about 7 to about 10 during precipitation is desirable for obtaininga good rate of conversion. Extraneous ions, such as halide ions, whichmay be introduced in preparing the slurry can, if desired, be removed byfiltering the alumina hydrogel, i.e., hydrous alumina, from its motherliquor and washing the filter cake with water.

The present invention is applicable to preparing calcined aluminaderived from hydrous alumina predominating in α-alumina monohydratehaving a crystallite size of less than 100A units. In order to achievethe maximum benefit from the present invention, it is preferred that theprecursor hydrous alumina predominate in α-alumina monohydrate having acrystallite size of less than about 70A units, more preferably less thanabout 60A units. Particularly outstanding results are achieved when theprecursor hydrous alumina predominates in boehmite having a crystallitesize in the range from about 10A units to about 60A units. The term"predominates in α-alumina monohydrate" as used herein refers to ahydrous alumina wherein more than 50%, preferably at least about 70% andmore preferably at least about 95%, by weight of the total aluminahydrate present is α-alumina monohydrate. The precursor hydrous aluminamay contain minor amounts of other crystalline forns in alumina, e.g.,gibbsite, bayerite, norstrandite and the like. Most preferably, however,the precursor hydrous alumina is essentially pure α-alumina monohydrateof the proper crystallite size.

The crystallite sizes referred to herein are those determined byconventional x-ray defraction analysis. More specifically, the sizes ofthe precursor hydrous alumina crystallites referred to herein are thosedetermined by x-ray diffraction techniques on samples dried atapproximately 100° C.

The amount of surface active agent present in the mixture of step (1) iseffective to increase the porosity of the product calcined alumina.Typically, the surface active agent is present in this mixture in anamount of at least 0.001% by weight based on the total amount of waterpresent, including water of hydration. It is preferred that the surfaceactive agent be present in the mixture of step (1) in an amount withinthe range from about 0.001% to about 5%, more preferably within therange from about 0.005% to about 1%, by weight based on the total amountof water present.

The drying of the slurry according to step (2) of the present method canbe accomplished in various manners -- for example, by drum drying, flashdrying, spray drying, tunnel drying and the like. The purpose of thedrying is to obtain a solid product which has a low enough free moisturecontent that it is suitable for macroforming, which is the next step inthe method. The extent of drying will depend, therefore, on the type ofmacroforming to be employed. Tabletting, for example, generally requiresa drier mix than does, say extruding, which usually calls for a freewater content of about 20 to 40 weight percent. The temperature at whichthe drying is performed is not critical but it is generally preferred tooperate at temperatures up to about 400° F. It may be -- because of thetype of equipment employed, or for whatever reason -- that it ispreferable to dry the mixture completely, or relatively so, and then addback sufficient water to obtain a formable, e.g., extrudable, mix. Suchan operation is within the purview of the instant invention and isintended to be embraced by the recitation: "drying the mixture to obtaina solid product which can be formed into macrosize particles."

Step (3) of the method, forming into macrosize particles, can beperformed, for example, by tabletting or extruding the solid product ofstep (2), as mentioned above. It is customary, especially in the case oftabletting, to incorporate in the mixture minor amounts of a dielubricant which is either non-deleterious to the calcined aluminaproduct or which can be removed by the subsequent calcining step. Oftenemployed, for example, are organic compounds which, by calcining theformed particles in an atmoshere having a controlled amount of oxygen,can be subsequently burned away without giving rise to excessivetemperature.

The size selected for the macrosized particles can be dependent upon theintended environment in which the calcined alumina particles are to beused as, for example, whether in a fixed of moving bed reactor system,etc. For example, when these alumina particles are to be used as acatalyst or catalyst support for use in reforming operations employing afixed bed of catalyst, these particles preferably have a minimumdimension of at least about 0.01 inch and a maximum dimension up toabout 0.5 inch or 1 inch or more. Alumina particles having a diameter ofabout 0.03 inch to about 0.25 inch, preferably from about 0.03 inch toabout 0.15 inch are often preferred, especially for use in a fixed bedreforming operation.

Calcining of the macrosize particles according to step (4) of theprocess is performed at temperatures sufficient to effect release ofwater of hydration from the particles. Generally suitable aretemperatures from about 600° F. to about 1200° F., preferably from about850° F to about 1000° F. The calcination can be effected in anoxidizing, reducing or inert atmosphere, the more economical use of adry air calcining atmosphere being preferred. It is usually advantageousto calcine in a flowing stream of the gaseous atmosphere. Pressure canbe atmospheric, super-atmospheric, or sub-atmospheric.

Where the macrosize particles contain significant amounts, say about 5%by weight or more, of uncombined water -- as, for example, will usuallybe the case where the particles have been formed by extrusion -- then,either as a separate operation or in the first stage of the calcination,the particles can with advantage first be dried at temperatures belowthe critical temperatures of water, which is about 705° F. Highertemperatures can cause fissures and rupture of the particles. Thus,prior to the particles being heated to as high as about 700° F.,preferably prior to being heated above about 400° F., their uncombinedwater content should be lowered to at least below about 15% by weight ofthe composition.

Surface active agents useful in the method of the present invention maygenerally be defined as those compounds having the ability to lower thetension prevailing at a given phase interface. In many instances,molecules of surface active agents include at least one hydrophobicportion and at least one hydrophilic portion. A wide variety of suitablesurface active agents are known to the art and include anionic, cationicand nonionic materials.

Included among the useful surface active agents are the anionic typeexemplified by the alkyl aryl sulfonates and alkenyl aryl sulfonateswhich contain from about 13 to about 20 carbon atoms per molecule. Alkylsulfonates and alkenyl sulfonates which contain from about 10 to about30 carbon atoms per molecule also are suitable as well as estersulfonates, amide sulfonates, sulfo fatty esters and primary andsecondary alkyl sulfates which contain from about 10 to about 30 carbonatoms per molecule.

Useful cationic surface active agents include quaternary ammoniumcomponents which contain from about 5 to about 30 carbon atoms permolecule.

Among the nonionic surfactants which are of particular usefulness in thepresent invention are

    R--(OC.sub.2 H.sub.4).sub.x --OH

and mixtures thereof wherein R is selected from the group consisting ofmonovalent hydrocarbon radicals containing from about 10 to about 50,preferably from about 14 to about 40, carbon atoms and x is an integerfrom about 2 to about 50, preferably from about 6 to about 30. Includedamong the monovalent hydrocarbon radicals are alkyl, such as decyl,tetradecyl, stearyl and the like; alkenyl such as decenyl, tetradecenyl,oleic and the like; alkaryl and polyalkaryl in which each of the alkylsubstituents contains from about 5 to about 18 carbon atoms such aspentyl phenyl, di pentyl phenyl, decyl phenyl, didecyl phenyl, stearylphenyl, penyl naphthyl, di penyl naphthyl, decyl di-phenyl and the like.In each instance, these radicals may include those non-hydrocarbonsubstituents which do not materially interfere with the surface activeproperties of the compound, for example, --OH, --NH₂, halide radicals,--SH and the like. These particularly useful nonionic surfactants may beprepared by conventional means, for example, by condensing ethyleneoxide with alcohols, alkyl phenols, fatty acids and the like.

Because the ionic surface active agents may contain metal or other ionsand may contaminate the final alumina product, it is preferred that thenonionic surface active agents be used when practicing the method of thepresent invention.

As noted previously, the alumina and alumina based particles prepared bythe method of the present invention may be of use as a catalyst and/orcatalyst support in various important processes, e.g., hydrocarbonreforming and hydrodesulfurization, hydrocarbon hydrocracking, paraffinand aromatic hydrocarbon isomerization and the like. In order to beuseful in certain of these processes, it may be necessary to add othercomponents to the alumina and alumina based particles of the presentinvention. Procedures for adding these various components to the aluminaand alumina based particles are conventional and well known to the artand, therefore, need not be reiterated here.

To illustrate the use of the alumina particles prepared by the method ofthe present invention as catalyst and catalyst support, a hydrocarbonreforming embodiment is described in detail as follows. In general,hydrocarbon reforming refers to a process whereby hydrocarbon feedstockcomprising paraffins and naphthenes is contacted in at least onereaction zone with a catalyst comprising a platinum group metal andalumina in the presence of free molecular hydrogen at hydrocarbonconversion conditions to yield a high octane and/or aromatics-richproduct.

A fully compounded hydrocarbon reforming catalyst can be obtained bytreating the alumina of the present invention with a platinum groupmetal component using any one of many conventional methods, such as ionexchange with the alumina, or by impregnation of the alumina at anystage in its preparation and either before or after the calcinationreferred to in step (4) of the present method. The preferred method foradding the platinum group metal to the alumina involves the use of awater soluble compound of the platinum group metal to impregnate thealumina following the calcination referred to in step (4). For example,platinum can be added to the calcined alumina by co-mingling thisalumina with an aqueous solution of chloro platinic acid. The platinumgroup metals include platinum, palladium, rhodium, ruthenium and thelike with platinum being preferred for use in the hydrocarbon reformingcatalyst. Generally, the amount of the platinum group metal present inthe final reforming catalyst is small compared to the quantities of theother components combined therewith. In fact, the platinum group metalcomponent generally comprises from about 0.05% to about 3%, preferablyfrom about 0.05% to about 1.0 %, by weight of the catalyst calculated onan elemental basis. Excellent results are obtained when the catalystcontains from about 0.2% to about 0.9% by weight of the platinum groupmetal.

Other components may also be included in the hydrocarbon reformingcatalyst. Among these added components are metals such as rhenium,germanium, iridium, tin and the rare earth metals such as cerium, withrhenium being preferred. When rhenium is included in the catalyst, it isnormally present in an amount from about 0.01% to about 5%, preferablyfrom about 0.05% to about 1.0%, by weight calculated as the elementalmetal. The rhenium component may be incorporated into the catalyst inany suitable manner and at any stage in the preparation of the catalyst.For example, the procedure for incorporating the rhenium component mayinvolve the impregnation of the alumina either before, during or afterthe time the platinum group metal is added. This impregnation may takeplace by co-mingling the alumina with an aqueous solution of a suitablerhenium salt such as ammonium perrhenate and the like or an aqueoussolution of perrhenic acid.

The fully compounded hydrocarbon reforming catalyst may also include ahalogen component. This combined halogen may be flourine, chlorine andbromine and mixtures thereof with flourine and particularly chlorinebeing preferred for the purposes of the present invention. The halogenmay be added to the alumina in any suitable manner either duringpreparation of the alumina or before or after the addition of thecatalytically active metallic components described previously. In anyevent, if the halogen is included, it is added in such a manner as toresult in a fully composited catalyst that contains from about 0.1% toabout 1.5%, preferably from about 0.6% to about 1.3% by weight ofhalogen calculated on an elemental basis.

When using the hydrocarbon reforming catalyst as prepared above, thehydrocarbon reforming system may comprise a reforming zone containing atleast one fixed bed of catalyst previously characterized. This reformingzone may be one or more separate reactors with suitable heating meansthere between to compensate for the net endothermic nature of thereactions that take place in each catalyst bed. The hydrocarbon feedstream that is charged to the reforming system may comprise hydrocarbonfractions containing naphthenes and paraffins that boil within thegasoline range. Typically, the hydrocarbon feed stream may comprise fromabout 20% to about 70% by weight of naphthenes and from about 25% toabout 75% by weight of paraffins. The preferred charge stocks are thoseconsisting essentially of naphthenes and paraffins, although in somecases aromatics and/or olefins may also be present. When aromatics areincluded in the hydrocarbon charge stock, these compounds comprise fromabout 5% to about 25% by weight of the total hydrocarbon charge stock. Apreferred class of charge stocks includes straight run gasolines,natural gasolines, synthetic gasolines and the like. On the other hand,it is frequently advantageous to charge thermally or catalyticallycracked gasolines including hydrocracked material or higher boilingfractions thereof, called heavy naphthas. Mixtures of straight run andcracked gasolines can also be used to advantage. The gasoline chargestock may be a full boiling range gasoline having an initial boilingpoint of from about 50° F. to about 150° F. and an end boiling pointwithin the range of from about 325° F. to about 425° F., or may be aselected fraction thereof which generally will be a higher boilingfraction commonly referred to as a heavy naphtha -- for example, anaphtha boiling in the range of about C₇ to about 400° F. In some cases,it is also advantageous to charge pure hydrocarbons or mixtues ofhydrocarbons that have been extracted from hydrocarbon distillates --for example, a straight-chain paraffin -- which are to be converted toaromatics. It is preferred that these charge stocks be treated byconventional pretreatment methods, if necessary, to remove substantiallyall sulfurous and nitrogenous contaminants therefrom.

In hydrocarbon reforming, reaction pressure in the range from about 50psig. to about 1,000 psig., preferably from about 100 psig. to about 600psig. is employed. Reforming operations may be conducted in the morepreferably pressure range from about 100 psig. to about 400 psig. Foroptimum reforming results, the temperature in the reaction zone shouldpreferably be within the range from about 700° F. to about 1100° F.,more preferably in the range from about 800° F. to about 1050° F. Theinitial selection of the temperature within this broad range is madeprimarily as a function of the desired octane of the final reformateconsidering the characteristics of the chargestock and of the catalyst.The temperature may then be slowly increased during the run tocompensate for the inevitable deactivation that occurs to provide aconstant octane product. In accordance with the hydrocarbon reformingprocesses sufficient hydrogen is supplied to the reaction zone toprovide from about 2.0 to about 20 moles of hydrogen per mole ofhydrocarbon entering the reaction zone with excellent results beingobtained when from about 7 to about 10 moles of hydrogen are suppliedper mole of hydrocarbon chargestock. Likewise, the weight hourly spacevelocity, i.e., WHSV, used in reforming may be in the range from about0.5 to about 10.0 with a value in the range from about 2.0 to about 5.0being preferred.

The following examples illustrate more clearly the method of the presentinvention. However, these illustrations are not to be interpreted asspecific limitations on this invention.

EXAMPLE 1

A water-hydrous alumina mixture was formed which contained 8.9% ofalumina (calculated as Al₂ O₃). The hydrous alumina used was a highpurity boehmite which had an average crystallite size of 40A. Acommercially available liquid, low foaming, nonionic surface activeagent having the following structural formula

    R--(OC.sub.2 H.sub.4).sub.x --OH

wherein R is an alkyl phenol radical containing an average of about 18carbon atoms and x is an integer having an average value of about 20 wasadded to this mixture such that this surface active agent amounted to0.0095% by weight of the total water present in the mixture. Thismixture was stirred at room temperature until completely uniform andthen spray dried at a gas outlet temperature of about 310° F. The spraydried product was made up of alumina hydrate particles, i.e.,microspheres, of sizes ranging from about 10 microns to about 100microns.

A sample of product A, i.e., 1700 grams, and 1250 ml. of water weremulled in a Simpson Intensive Mixer for a sufficient length of time toinsure a completely uniform mixture. The mixture was then extrudedthrough a 1/16 inch die plate using a double auger extruder. Theextruded product was dried for about 24 hours at 250° F. in a forceddraft oven. The dried product was then broken into particles about 1/4inch in length and screened free of fines. The dried product was thencalcined in an electric muffle furnace using an automatic controller togive a temperature rise of 300° F./hour to 1050° F., a 3 hour holdingtime at 1050° F. and rapid cooling to yield a first extruded product.The total pore volume of this extruded product, as measured by an He/Hgporosimeter, was 0.468 ml./gm.

A second extruded product was prepared in the same manner as aboveexcept that no surface active agent was employed. The total pore volumeof this product was only 0.421 ml/gm. Therefore, the first extrudedproduct had about 11.2% more total pore volume than the second extrudedproduct.

EXAMPLE 2

This example illustrates an alternate method for preparing the hydrousalumina for further processing by the method of the present invention. Asolution of 25 lbs. of AlCl₃.6H₂ O in 51 liters of deionized water isformed. 20 liters of ammonium hydroxide solution containing equalvolumes of water and of 0.90 specific gravity ammonium hydroxide isadded to the previously formed mixture. Approximately 35 minutes elapsedtime is used to effect this addition. After additional stirring, aprecipitate is separated in a plate and frame press to form a firm cake.This cake is broken up into approximately 1 inch cubes and is placedinto a vessel of deionized water and washed by perculation, i.e.,running deionized water past the cake at about 20 gallons per hour.Washing is continued for approximately 100 hours.

X-ray diffraction patterns of the resulting hydrous alumina samplesindicate this product to be approximately 95% boehmite having acrystallite size in the range of from about 30A to about 50A, plus asmaller amount of gibbsite.

Using this hydrous alumina, a water hydrous alumina mixture is formedwhich contains about 9.0% by weight of alumina (calculated Al₂ O₃). Thesame commercially available surface active agent used in Example 1 isadded to the water hydrous alumina mixture that the surface active agentamounts to about 0.01% by weight of the total amount of water in themixture. This mixture is stirred at room temperature until completelyuniform and then is spray dried at a gas outlet temperature of about310° F. This spray dried product is made up of alumina hydrate particlesof sizes ranging from about 10 microns to 100 microns.

Using these spray dried particles in a procedure similar to that givenin Example 1, an extruded product is prepared. An additional extrudedproduct is prepared in an identical manner except that no surface activeagent is employed. It is found that the extruded product produced usingthe surface active agent has about 11% more total volume than theextruded product prepared using no surface active agent.

The alumina and alumina-based particles having increased pore volumeobtained by the method of the present invention when used as catalyst orcatalyst supports in many instances provide improved performance, e.g.,catalytic activity.

While this invention has been described with respect to various specificexamples and embodiments, it is to be understood that the invention isnot limited thereto and that it can be variously practiced within thescope of the following claims.

The embodiments of the invention in which an exclusive property orprivilege is claimed are defined as follows:
 1. In a method forreforming a hydrocarbon feedstock comprising paraffins and naphthenes inat least one reaction zone with a catalyst comprising platinum groupmetal and alumina in the presence of free molecular hydrogen athydrocarbon conversion conditions, the improvement which comprises usingalumina prepared by a method which comprises:(1) forming a mixture of anaqueous slurry of hydrous alumina and at least one surface active agent,said hydrous alumina predominating in α-alumina monohydrate having acrystallite size of less than 100A, said surface active agent beingpresent in the mixture in an amount sufficient to increase the porosityof the calcined alumina hereinafter described; (2) drying said mixtureto obtain a solid product which can be formed into macrosized particles;(3) forming said solid product into macrosized particles; and (4)calcining said macrosized particles to form calcined alumina havingincreased porosity.
 2. The method of claim 1 wherein said surface activeagent is present in the mixture formed in step (1) in an amount withinthe range from about 0.001% to about 5% by weight based on the totalamount of water present in said mixture and the mixture formed in step(1) contains from about 1% to about 50% by weight of alumina, calculatedas Al₂ O₃.
 3. The method of claim 2 wherein said surface active agent ispresent in the mixture formed in step (1) in an amount within the rangefrom about 0.001% to about 5% by weight based on the total amount ofwater present in said mixture and the mixture formed in step (1)contains from about 1% to about 50% by weight of alumina, calculated asAl₂ O₃.
 4. The method of claim 3 wherein at least 95% by weight of thetotal alumina hydrate present in the mixture formed in step (1) isα-alumina monohydrate having a crystallite size of less than about 70A,said surface active agent is present in the mixture formed in step (1)in an amount within the range from about 0.001% to about 1% by weightbased on the total amount of water present in said mixture and themixture formed in step (1) contains from about 1% to about 16% by weightof alumina, calculated as Al₂ O₃ and said surface active agent isnonionic.
 5. The method of claim 4 wherein said surface active agent isselected from the group consisting of

    R--(OC.sub.2 H.sub.4).sub.x --OH

and mixtures thereof wherein R is selected from the group consisting ofmonovalent hydrocarbon radicals containing from about 10 to about 50carbon atoms and x is an integer from about 2 to about
 50. 6. The methodof claim 2 wherein at least 70% by weight of the total alumina hydratepresent in the mixture formed in step (1) is α-alumina monohydratehaving a crystallite size of less than about 70A.